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Hello, I've been finally getting around to learning Houdini constraints and motors. Here's a first set of tests that I've ran. They are all quite simple beginnings, but I've learnt alot, particularly about ways to generate constraints in SOPS and then apply to DOPS, which seems really powerful.

Im also using this to have a little peek at mantra, and learn how to set up really simple scenes.

Heres the hip files for anyone else trying to work this stuff out. They are a bit disorganised, and alot of them contain ROPS that will need to be rerendered.

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I've done some more tests with motors. This time trying to create a bunch of them procedurally at once. Getting all the name attributes to line up was a little tricky on some of them, but I understand all this so much better after doing this.

Getting the axis of the motors to do what I want was also a bit tricky, but I've mostly cracked it now.

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In case this is useful for anyone, I recently had a few misunderstandings about how pin constraints work in rotation mode. Heres a simple file with a bunch of basic constraints setup with packed primitive, and regular rbd objects. Both SESI and a helpful chap over in this thread recommended the conetwist constraint instead - which works well in the tests ive ran so far.

It makes a good hinge joint, and you can layer on a world aligned rotational spring constraint if you want to make it springy.

Here's an example of a few useful setups. The examples colored red are an example of what not to do.... Its a gif so click on the piccie to see the constraints in action. (its not very exciting)

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Recently I wanted to make constraints based on impacts. I finally managed it. Here's the basics of the system. It uses a couple of ForeEach SOPs to step through and delete any constraint between the same two rbd's.

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I assumed creating constraints at the position of the impact would be easy. NOPE! You have to transform each impact point into the rest position(Easy) AND the rest orientation(NOPE!). Luckily i'd done this about 100 years ago and I vaguely remembered how.

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I made some renders using the constraints on impacts setup I made. The sims are pretty crappy, but the basics of the system seems to work solidly enough. It would just be a matter of tweaking all the settings to get a smoother result.

Each pair of RBDs gets no more than 1 constraint. I think it might work better if I allowed a few more, as the RBDs can spin around on this constraint, which looks a bit unstable.

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I have a hip file I use a bunch which contains some of the common tricks I always need, but constantly forget how to do. I thought i'd share it. Mostly its VEX/VOPS stuff to manipulate point transforms, a lot of it revolves around creating and using the orient attribute.

I'll update it as I go I imagine. When I discover something new, I plan to throw it in here to prevent it eroding from my brain.